Amniotic fluid pressures in severe twin-twin transfusion syndrome

Objective The objective of this study was to assess simultaneously the amni otic fluid pressure in the sacs of the recipient and the donor twin in pati ents with severe twin-twin transfusion syndrome. Materials and methods Patients with stuck-twin syndrome undergoing laser su rgery were enrolled in the study. The sac of the recipient twin was entered with a 3-mm trocar. A neonatal pressure monitor with a column of normal sa line was used to measure the amniotic fluid pressure. Pressure was measured by connecting the fluid line to the luer lock on the trocar after allowing for stabilization. The amniotic fluid pressure in the sac of the donor twi n was measured in the same way after performing a separate amniocentesis in this sac with a 22-gauge needle without traversing the dividing membrane. The pressure measurements were repeated at the end of surgery in some cases . Results Seven patients were enrolled in the study. The mean amniotic fluid pressure in the sac of the recipient twin was 10.67 mmHg (SD 3.98), and 10. 5 mmHg (SD 4.64) in the sac of the donor fetus, with individual pressure di fferences of 1-3 mmHg. This difference was not statistically significant (p > 0.05, Student's t test). Conclusions Amniotic fluid pressures are similar in the sacs of the recipie nt and donor twin. These data are in agreement with the basic theory of ela sticity, which holds that the difference in pressures only occurs while the dividing membrane is under tension. After the external chamber has increas ed its capacity, the pressure differential between the chambers disappears, and the tension in the membrane is zero. Our data do not support the ratio nale of 'equalizing the pressures' between the two sacs by removing, adding , or purposely disrupting the dividing membrane to allow transfer of fluid between the two amniotic cavities as a method of treating twin-twin transfu sion syndrome.